SCIENCE / MEDICINE : Researchers Succeed in Adding Gene to Fertile Corn

Researchers at a Cambridge, Mass., genetic engineering firm revealed last week that they have for the first time inserted an extra gene into corn plants and, at the same time, enabled the plants to remain fertile so the gene is passed along to progeny.

The discovery opens the door to altering the heredity of corn plants to increase their resistance to insects, introduce resistance to herbicides and drought and increase the nutritional value of corn. The discovery could have global agricultural significance because corn varieties account for 24% of all seeds sold throughout the world.

The discovery is even more important because corn belongs to a family of plants, called monocots, that includes wheat, rice and most of the world’s other important cereal grains. Scientists have not previously been successful in using genetic engineering techniques to introduce new traits into monocots.

Monocots put forth one leaf (cotyledon) when the seed first sprouts. Dicots, the family that includes most of the plants now used for genetic engineering studies, such as tobacco, pansies and tomatoes, put forth two leaves. Dicots have proved relatively easy to work with, but monocots have been largely intractable.

“Useful corn transformation with the production of fertile plants that transmit the gene to succeeding generations has been an insurmountable roadblock for agricultural biotechnology,” said molecular biologist Ralph Hardy of Cornell University. “For the first time, the company’s scientists can apply the tools of genetic engineering to the most important U.S. grain crop, corn.”

Officials of the company, BioTechnica International, have so far refused to reveal what gene was inserted into the corn or how it was introduced, pending the receipt of a patent.

Other researchers speculate, however, that they used one of two techniques, called shotgun cloning and electroporation, to get the added gene past the thick cell wall of the monocots.

In shotgun cloning, the gene is deposited on the surface of small Teflon pellets that are fired at the cells by a shotgun-like device. In electroporation, an intense electrical field is used to open small pores in the cell membrane and force the gene through.

In either case, the company may have used new technology to encourage the added gene to insert itself in a desirable location in the host cell’s deoxyribonucleic acid, or DNA, its genetic blueprint.

Among the genes that BioTechnica has said it would like to insert into corn is one that serves as a blueprint for a protein called cow pea trypsin inhibitor, which provides increased resistance to insects.

The company said it would also like to insert genes for the amino acids tryptophan and lysine, which are not normally produced in corn. Adding those genes would increase the corn’s nutritional value for farm animals and for humans.

The company said it would apply to the U.S. Department of Agriculture for permission to field test the genetically engineered corn this year.